The invention is based on a fuel injection valve for internal combustion engines as generically defined by the preamble to claim 1. One such fuel injection valve, known from German Patent Disclosure DE 196 23 211 A1, has a valve body in which, in a bore, a piston like valve member is disposed such that it is movable axially counter to the force of a closing spring. On the end toward the combustion chamber, the valve member changes over into a closing head, which is guided in the bore. In the outward-oriented opening stroke motion of the valve member, the closing head emerges from the bore, and a control edge embodied on the closing head uncovers at least one injection opening. A plurality of injection openings can also be provided, which are opened successively by the control edge. As a result, by a limitation of the opening stroke of the valve member to a partial stroke, it becomes possible to uncover only some of the injection openings or to open only a partial cross section of one injection opening, and thus to control the entire effective injection cross section as a function of the opening stroke of the valve member. The opening stroke motion is limited to a partial stroke by a control piston, disposed in the valve body, whose end face defines a hydraulic control chamber. The control chamber can be filled with fuel at high pressure and as a result can displace the control piston axially from a first stroke position to a second stroke position, as a result of which the valve member executes either the maximum stroke or only a partial stroke. A hydraulically adjustable stroke stop of this type has a black-and-white function; that is, it does not allow any graduations between the two opening strokes. This limits the control capability of the fuel injection event, making further optimization of the injection event more difficult.
In a fuel injection valve of the inward-opening type as well, such as that known from German Patent Disclosure DE 197 29 843, it can be desirable for the sake of precise metering of a preinjection quantity to have a partial stroke available that has more than a black-and-white function, allowing an optimal injection course to be attained.
The fuel injection valve of the invention for internal combustion engines, having the characteristics of the body of claim 1, has the advantage over the prior art that between the closing spring and the guided portion of the valve member, a combined hydraulically and piezoelectrically controlled stroke stop is embodied, with which the opening stroke motion of the valve member can be set to any value between the maximum opening stroke and the partial stroke. By combining the hydraulically adjustable piston with a piezoelectric actuator, it is possible to switch the hydraulic piston not only between maximum stroke and partial stroke but also, by the delivery of electric current to the piezoelectric actuator, to switch it between the partial stroke and any arbitrary value between partial stroke and the maximum opening stroke of the valve member. As a result, in a further performance graph range of the engine, an optimally adapted opening stroke of the valve member is feasible. If switching between only partial stroke and a maximum opening stroke is necessary, then the piezoelectric actuator need not be supplied with electric current, which is advantageous from an energy standpoint.
Besides the use of the combined hydraulic and piezoelectrically controlled stroke stop in an outward-opening vario-nozzle, it is also possible to use the subject of the invention in an inward-opening fuel injection valve in the same advantageous way.
In an advantageous feature of the stroke stop, the control piston is embodied as a hollow cylinder, on the end of which remote from the combustion chamber the piezoelectric actuator is disposed.
This makes it easy to mount the control piston, since the piezoelectric actuator and the non-piezoelectrically active part of the control piston can be installed separately. In a control piston embodied in this way, in a further advantageous feature, the valve member in the opening stroke motion does not come into direct contact with the piezoelectric actuator but only with the interposition of a shim. This results in less wear on the piezoelectric actuator and thus a longer service life of the hydraulic stroke stop. Furthermore, the shim offers the capability, by replacement of this simple and hence economically produced shim, of setting the maximum opening stroke precisely by way of the thickness of the shim.
In a further advantageous feature, the control pressure for controlling the hydraulic stroke stop is drawn from a control line, which communicates with a high-pressure reservoir via a control valve. Furthermore, via a further control valve, the control line communicates with the largely pressureless fuel tank, so that by suitably triggering the two valves, loading and relieving of the control line are possible, without requiring a further high-pressure fuel source.
Further advantages and advantageous features of the subject of the invention can be learned from the description, drawing and claims.